Various attempts have been made to synchronize the transition of disco or "house" music from one turntable to another. For example, U.S. Pat. No. 4,300,225 of Lambl describes an electronic device to alert a disc jockey that two beats of the songs are in synchronization, by providing a light at the moment of synchronization. However, the Lambl '225 device does not give the disc jockey lead time to predict when the synchronization will occur.